Why go to Mars in the first place? Mars was once a warm/wet planet like Earth. It's the most earth-like planet in the Solar System. Now Mars is very, very cold & overall drier than the Sahara desert here on Earth. What happened? Did life have time to evolve? Is there still some kind of life on Mars (I say 99.9% chance YES!)? By exploring other planets we learn so much about US and this planet that most people just don't get.
The most commonly heard criticism about the space program is that we should "spend our money" here on Earth. That money IS spent here on Earth. Employing thousands of high-tech positions creating cutting-edge technologies. The United States - and the World - has benefited immensely because of the space program. PC's; most modern electronics; the Internet; medicines; transportation etc. would not currently exist if not for our space program. The $$$ payout was/is in the billions. The payback? Direct/indirect In the TRILLIONS.